The present invention relates to a bonding material composition used for unitarily joining a plurality of members such as honeycomb segments constituting a honeycomb structure, a joined body integrated with the bonding material composition, a method for manufacturing the bonding material composition, and a method for manufacturing the joined body using the bonding material composition.
A honeycomb structure is widely used as a trapping filter for exhaust gas, for example, a diesel particulate filter (DPF) for trapping and removing particulate matter contained in exhaust gas from a diesel engine or the like.
Such a honeycomb structure has a structure having a numerous number of cells which functions as fluid passages, and are defined by porous partition walls of, for example, silicon carbide (SiC) are disposed in parallel with one another. Further, end portions of adjacent cells are alternately plugged like in a checkered pattern. That is, for example, one end portion of a cell at one side is open and another end portion thereof is plugged, and the end portion of another cell adjacent to the open end portion of the above-mentioned cell is plugged, but the other end portion of the another cell is open.
Such a structure enables exhaust gas to be purified by allowing exhaust gas to flow into predetermined cells (inflow cells) from one end, to pass through porous partition walls, and to be discharged from the cells adjacent to the inflow cells (outflow cells) in order to trap particulate matter in exhaust gas with the partition walls when the exhaust gas passes through the partition walls.
In order to use such a honeycomb structure (filter) continuously for a long period of time, it is necessary to regularly subject the filter to a regeneration treatment. That is, in order to reduce a pressure loss increased by particulate matter accumulated in the filter with the lapse of time to put the filtering performance in the initial state, it is required to remove the particulate matter accumulated in the filter by combustion. However, there is a problem of causing defects such as cracks or breakages in a honeycomb structure due to large thermal stress generated at the time of regeneration of a filter. In order to cope with the demand for improvement of thermal shock resistance against the thermal stress, there has been proposed a honeycomb structure having a segmented structure imparting a function of dispersing and relaxing the thermal stress by unitarily joining a plurality of honeycomb segments with a bonding material layer. Thus, the thermal shock resistance could be improved to some extent.
However, a demand for further enlargement of a filter has been increasing in recent years, and thermal stress generated upon regeneration has been increasing due to this tendency. Therefore, in order to solve the above problem, further improvement in thermal shock resistance as a structure has strongly been desired. In order to realize the improvement in thermal shock resistance, a bonding material layer for unitarily joining a plurality of honeycomb segments is required to have excellent stress-relaxing function and bonding strength.
There has conventionally been disclosed a ceramic structure formed by unitarily joining a plurality of honeycomb segments with a sealing agent containing at least inorganic fibers, an organic binder, an inorganic binder, and inorganic particles, the inorganic fibers having an orientation of 70% or more (see JP-A-2002-177719).
In such a ceramic structure, an effect of inhibiting a filter (ceramic structure) from expanding and contracting can be obtained by using a sealing agent (bonding material composition) as described above, and thermal stress applied on the filter can be released even under severe use conditions. However, in the case that the bonding material composition contains orientated inorganic fibers as described above, high thermal stress generates because of the high tensile Young's modulus (elastic modulus measured by tensile test) while the compressive Young's modulus (elastic modulus measured by compression test) in the thickness direction of the bonding material layer is low. In addition, in the case that members to be joined are joined with orientating fibers in one direction in the bonding material composition, expansion and contraction of the bonding material composition upon drying or a thermal treatment is different between the direction of the orientation and the direction perpendicular to the orientation of the fibers, which is prone to cause defects such as cracks and voids.
Further, in case of the sealing agent disclosed in JP-A-2002-177719, there is a problem that the cost should unavoidably increase since it is ceramic cement which requires the control of the characteristics thereof by regulating the diameter or length of fibers functioning as filler. Furthermore, since the sealing agent employs fibers as filler for the ceramic cement, there might be a potential risk to a human body due to the use of fibers.